Treatment of an oil/grease wastewater using ultrafiltration: Pilot-scale results

Wastewater containing about 0.5% oil and grease (O/G) from a metal industry was treated by tubular ultrafiltration using membranes having a molecular weight cutoff (MWCO) of 120,000 and a negative surface charge (P membrane) and of 100,000 and no surface charge (M membrane), Permeate flux decreased dramatically during the first several hours of operation and then leveled-off for the remainder of semibatch operation. The average P membrane flux was significantly higher than the M membrane (38 versus 27 gal/ft(2).d) because of its higher MWCO and negative surface charge. Increasing the transmembrane pressure and crossflow velocity increased the permeate flux for both membranes. O/G concentrations less than 50 mg/L and total suspended solids (TSS) levels less than 25 mg/L were common for both membranes. O/G removal efficiencies (rejections) averaged 98% for the M membrane and 97% for the P membrane. TSS rejections were approximately 97% for both membranes. Effluent O/G concentration and turbidity from the P membrane were slightly higher than the M membrane because of the P membrane's higher MWCO and the larger flux. The average volume reduction and residual production were 97% and 32 gal/1000 gal, respectively, Acid cracking of the concentrate with sulfuric acid was marginally successful.